Sealed pressure switch



Jin. 8, 1963 K. D. SHAUB ETAL 3,072,762

SEALED PRESSURE SWITCH Filed Feb. 3, 1960 F1G.l.

ATTORNEY INVENTORS' 3,072,762 SEALED PRESSURE SWITCH Kenneth D. Shaub, Timonium, and William W. Wotell, Parkville, Md., assignors to The Bendix Corporation, a corporation of Delaware Filed Feb. 3, 1960, Ser. No. 6,511 8 Claims. (Cl. ZOO-83) switches may be required to respond quickly and with a high degree of accuracy to changes in pressure while at the same time they must be capable of withstanding severe vibrational and gravity stresses, otherwise the circuit to be controlled may be made or broken prematurely. When the switch is located at a point more or less distant from the actuating pressure, necessitating a sensing chamber and conduit system of appropriate length, it

- isimportant that such chamber be made as small as is structurally permissible to ensure a minimum lag in response for a given pressure change. Another .factor .-which affects response and accuracy is loading of the .diaphragm or diaphragms by relatively heavy contact structure and associated terminals and seals.

An object of the instant invention is to produce a sealed pressure switch of the type disclosed in the patent to .Dunmyttr and Wood, No. 2,671,833, having improved response characteristics over a wide range of ambient pressure, resulting from utilization of a single diaphragm and a particular type of contact structure which is light i in weight and hence reduces loading to a minimum and at the same time provides strong and rugged contacts and a perfectly balanced diaphragm.

Another object is to provide a switch of the type specified in which the sensing chamber may be extremely low volume substantially independent of the size of the reference-pressure chamber and associated components.

United States PatentO ice ing action. This enables the spacing of the plates to be adjusted when setting the contacts, to be described. The opposite edges of the plates are connected by an adjustable screw shaft 13, having a knurled or gear head, which when the switch is adapted for remote control, may have a driving connection with a servo motor or the like. A spring 13' biases the plates apart. These supporting plates may be made of a good grade of stainless steel or other suitable material. The plate 10 is provided with a central annular recess, in which is seated a terminal plate 14, adapted to support an electrical contact element 15, having a stem 15', which projects through said plate and also a seal 16 and has fixed on its outer end a terminal 17, to accommodate an electrical lead wire 18.

The opposite plate 11 is also formed with a central opening, circumferentially relieved or recessed to receive the peripheral edge of a diaphragm 19, fixed to the plate by means of a weld ring 20. Diaphragms such as that shown at 19, when used in switches of the type under consideration, are made for high precision service; in practice they are fabricated from a high grade of sheet metal sold under the trade name of Ni-Span C.

Overlying the diaphragm 19 is a cap 21, having its peripheral edge seated in another annular recess formed in the plate 11 and held in place by means of a weld ring 22. The cap 21 in conjunction with the diaphragm .19 defines a sensing chamber C, which is preferably re- ,duced in volume as much as is structurally permissible A further object is to provide a light-weight sealed pressure switch of the type specified so constructed as -to provide a reference-pressure chamber and a sensing chamber separated by asingle diaphragm carrying alight yet strong and rugged contact element adapted to coact with a mating contact firmly supported on arelatively fixed member, capable of resisting vibrational and acceleration stresses and externally adjustable to set the con- .tacts, the latter being readily adapted to make and/or.

break at some preselected ambient pressure.

.The foregoing and other objects and advantages will become apparent in view ofthe following description taken in conjunction with the drawing whereint,

FIGURE 1 is a view in sectional elevation of a makeon-ascent switch according tothe invention, taken substantially on the line 11, FIGURE 2; I

FIGURE 2 is a side elevation of FIGURE 1; it could also be considered a top plan view of FIGURE 3;

FIGURE 3 is a broken perspective. of theswitch shown in FIGURES l and 2; and

FIGURE 4 is a central fragmentary section of the switch shownin FIGURES 1, 2 and 3 but provided with a contact structure which adapts the switch to both make and break an associated electric circuit over a given range of varying environmental pressure.

Referring to the drawing and first to FIGS. 1, 2 and 3, the switch assembly comprises a pair of capsule-supporting plates 10 and 11, hingedly conected in spaced relation when the pressure to be sensed is communicated by suitable tubing to said chamber from a point remote from where the switch may be installed. The purpose of the fitting F is to accommodate such tubing.

An electricalcontact-supporting member 23, carrying a contact element 23', is connected to the central portion of the diaphragm 19 by means of a seal 24, through which the stem 23 of the contact projects. This seal should be made of material capable of bonding to the adjacent portion of the diaphragm. There are glass seals obtainable in the open market for this purpose. The outer end of the stem 23 has connected thereto a leaf spring terminal lead 25, which extends laterally and connects with a seal and terminal'member 26, bonded to the cap 21, said member having a stem which projects exteriorly of the cap and has connected to its outer end a clip 27, which accommodates a lead wire28, which like the lead wire 18 extends to the'circuit to be controlled.

It will be noted that the contact-supporting member 23 ,i is in the form of an open-ended yoke or stirrup, bridged at, its free ends by the rod-shaped contact element 23, which latter may be of the precious metal type, for example platinum, having its opposite ends fixed as by it is relatively strong and rugged and together with the element 23 provides a closed loop, defining an opening to receive the contact 15, which may also be of precious "metal, the position of the contact 15 being adjustable by varying the spacing of the capsule plates 10 and 11. Since the contact 15 is fixed to the relatively stationary plate 14, which in turn is connected to the heavier plate 10, it will be substantially free of vibrational and acceleration stresses, the diaphragm 19 being the only movable or pressure-responsive part of the entire assembly.

A flexible Wall member in the form of a bellows 30 is connected atits opposite ends to the inner free edges of the plates 10 and 11, and together with the diaphragm 19 and plate 14 defines a reference-pressure chamber C, which may be evacuated and/or loaded with a suitable inert gas by means of the tube 31.

The open holes in the capsule plates 10 and 11, one of which is indicated at 32, are for mounting the said 3 plates to additional supporting members, not shown, or to any other suitable support.

Operation The switch of FIGS. 1, 2 and 3 is what may aptly be termed a makeon-ascent switch. For example, let it be assumed that the circuit to be controlled is to remain deenergized at sea level and to be energized at some given altitude. When the switch is assembled, the

lower contact 15 (as viewed in FIG. 3) is projected through the open stirrup 23. Since the spacing of the contacts 15 and 23' may be set externally by the screw 13, it becomes a relatively easy matter to calibrate the switch. The sensing chamber C may be connected to the source of pressure to be sensed, or in certain instances where the switch is mounted directly in the region of such pressure, the cap may be omitted and the external lead wire connected directly to the conductor 25. As altitude is gained and the external or ambient pressure decreases, the diaphragm 19 flexes outwardly until, when the preselected pressure is reached, contact is made and the circuit to be controlled is completed.

The stirrup-shaped contact support 23 not only has the;advantages of being a relatively strong yet extremely light element; it provides a perfectly balanced member, which would not be the case were it shaped in a manner similar to the contact 15 and its supporting stern 15'.---Single diaphragm construction not only reduces the tendency towards inaccuracy due to vibration and acceleration stresses, but it also lowers the cost of the assembly, since high-precision diaphragms require considerable care in fabrication and have a high rate of rejjection. The switch as a whole may be made small and compact; the one shown in FIGS. 1, 2 and 3 is about three times actual size of a switch currently in production.

FIGURE 4 member 34, hinged at 35 to the plate 14 and having its free end connected to said plate by means of a set screw 36. The opening around-the stem 33' is sealed by means of a flexible bellows 37, which at one end is secured by a suitable seal 38 to the member 34 and its opposite end to the plate 14. In this arrangement, both contacts 15 and 33 may be simultaneously reset by adjustingthe spacing of the plates and 11 in the same manher as in FIGS. 1, 2 and 3, while the contact 33 may be reset independently of the contact 15 by means of the screw 36, both adjustments being accessible exteriorly of the switch. In the position shown in FIG. 4, it can be assumed that the switch is set to leave both circuits controlled by the contacts 15 and 33 open at some given pressure, and on ascent, contacts 23' and 15 will engage at a given altitude, and upon descent, contact 23' will break with 15 and subsequently make with 33. However, it will be obvious that one or more circuits could be controlled in other ways by a multiple of relatively fixed but adjustable contacts coacting with the pressureresponsive contact 23.

From the foregoing it will be seen that a balanced, highly-sensitive sealed pressure switch is provided, capable of accurate electrical switching over practically any selected pressure or altitude range. The single pressureresponsive member or diaphragm is supported by relatively heavy elements which may be rendered substantially free from errors due totemperature changes, and

the sensing chamber C may be made small or of a reduced volume to avoid lag where the switch is connected by piping of varying lengths to the pressure to be sensed.

What we claim is:

1. In a pressure-responsive electrical switch, a first substantially rigid capsule-supporting member having an opening therein, a diaphragm movable in response to pressure differentials thereacross overlying said opening and having its peripheral edge secured to said member, a second coacting substantially rigid capsule-supporting member mounted in spaced relation to said first supporting member, a flexible wall member connecting said supporting members and together with the latter and said diaphragm defining a sealed chamber, a first contact element fixed centrally of said diaphragm and projecting into said chamber, and a second contact element fixed to said second supporting member and also projecting into said chamber for coaction with said first contact element such that said first element closes against said second element with decreases in the pressure sensed by said diaphragm exterior of said chamber, and means for setting the spacing of said supporting members to set said contact elements.

2. A switch as claimed in claim 1 wherein said first contact element is in the form of a closed loop of conductive material providing an opening into which said second contact element projects.

3. A switch as claimed in claim 1 wherein said first contact element is in the form of an open-ended generally stirrup-shaped piece of conductive material with a contact bridging said ends and providing a closed loop defining an opening into which said second contact element projects.

4. A switch as claimed in claim 1 wherein a cap 0 substantially rigid non-pressure-responsive material overlies said diaphragm and is secured to said first supporting member in spaced relation to the diaphragm, providing a sensing chamber adapted for communication with the pressure being sensed.

5. In a pressure-responsive electrical switch, a first rigid capsule-supporting plate having an opening therein, a diaphragm movable in response to pressure differentials thereacross overlying said opening and having its peripheral edge secured to said plate, a second coacting capsule-supporting plate mounted in spaced relation to said first plate, a collapsible Wall member connecting said defining a sealed reference chamber, a first contact element fixed centrally of said diaphragm and projecting into said chamber, a second contact element fixed ce'ntrally of said second plate and also projecting into said chamber for coaction with said first contact element such that said first contact element is moved in a closing direction with respect to said second contact element with decreases in the pressure sensed by said diaphragm, a cap of substantially rigid material overlying said diaphragm and having its peripheral edge secured to said first plate, said cap being spaced from said diaphragm to define a sensing chamber adapted for communication with the pressure to be sensed, and means for adjusting the spacing of said plates to set said contacts.

6. A switch as claimed in claim 5 wherein the contact element carried by said diaphragm is in the form of a yoke of conductive material having forked ends bridged by a contact member and forming a closed loop with said second contact projecting into the opening defined by the loop.

7. In a pressure-responsive electrical switch, a first subcontact fixed centrally of said diaphragm and project ing into said chamber, a second contact fixed centrally of said second plate and also projecting into said chamber for coaction with said first contact, said first contact being in the form of a generally yoke-shaped substantially closed loop defining an opening into which said second contact projects such that said first contact is moved toward said second contact with decreases in the pressure sensed by said diaphragm, a third contact also carried by said second plate and projecting into said chamber exteriorly of said loop for coaction with the diaphragm contact in conjunction with said second contact, and means 'for resetting the spacing of said plates to set the make and/or break positions of the contact.

8. A switch as claimed in claim 7 wherein said third contact is carried by a member adjustably connected to said second plate and projects through a sealed opening in the latter into said chamber, said last-named member being adjustable to reset said third contact independently of said second contact.

References Cited in the file of this patent UNITED STATES PATENTS 2,658,120 Murphy Nov. 3, 1953 2,671,833 Dunmyer et a1. Mar. 9, 1954 2,761,927 Szypulski Sept. 4, 1956 2,943,167 Hughes et a1, June 28, 1960 

1. IN A PRESSURE-RESPONSIVE ELECTRICAL SWITCH, A FIRST SUBSTANTIALLY RIGID CAPSULE-SUPPORTING MEMBER HAVING AN OPENING THEREIN, A DIAPHRAGM MOVABLE IN RESPONSE TO PRESSURE DIFFERENTIALS THEREACROSS OVERLYING SAID OPENING AND HAVING ITS PERIPHERAL EDGE SECURED TO SAID MEMBER, A SECOND COACTING SUBSTANTIALLY RIGID CAPSULE-SUPPORTING MEMBER MOUNTED IN SPACED RELATION TO SAID FIRST SUPPORTING MEMBER, A FLEXIBLE WALL MEMBER CONNECTING SAID SUPPORTING MEMBERS AND TOGETHER WITH THE LATTER AND SAID DIAPHRAGM DEFINING A SEALED CHAMBER, A FIRST CONTACT ELEMENT FIXED CENTRALLY OF SAID DIAPHRAGM AND PROJECTING INTO SAID CHAMBER, AND A SECOND CONTACT ELEMENT FIXED TO SAID SECOND SUPPORTING MEMBER AND ALSO PROJECTING INTO SAID CHAMBER FOR COACTION WITH SAID FIRST CONTACT ELEMENT SUCH THAT SAID FIRST ELEMENT CLOSES AGAINST SAID SECOND ELEMENT WITH DECREASES IN THE PRESSURE SENSED BY SAID DIAPHRAGM EXTERIOR OF SAID CHAMBER, AND MEANS FOR SETTING THE SPACING OF SAID SUPPORTING MEMBERS TO SET SAID CONTACT ELEMENTS. 